Field of the Invention
The present invention relates to certain proteins which may be involved in regulating physiological changes (e.g. changes in cell-cell adhesion) and to uses thereof.
Cell adhesion is important for a wide variety of regulatory and developmental processes. The cadherins comprise a family of transmembrane, cell surface glycoproteins that mediate Ca.sup.2+ -dependent cell-cell adhesion in a homotypic manner (Takeichi, 1991). In cells with well developed intercellular junctions, the cadherins are localized to the adherens junction (Boller et al., 1985) but appear to influence other intercellular junctions such as gap junctions (Matsuzaki et al., 1990; Musil et al., 1990) and tight junctions (Gumbiner and Simons, 1986; Gumbiner et al., 1988). The adherens junction also plays a crucial role in the development and maintenance of cell polarity (see Nelson, 1992) and its dysfunction has been strongly implicated in the invasiveness and carcinogenesis of tumour cells (see e.g. Behrens et al., 1989; Frixen et al., 1991; Vleminckx et al., 1991; Shimoyama et al., 1992; and Hedrick et al., 1993; Tsukita et al., 1993; Birchmeier and Behrens, 1994).
The conserved cytoplasmic domain of cadherins is known to associate with three proteins, termed .alpha.-.beta.-and .gamma.-catenin (Pzawa et al., 1989), which serve to link cadherins to the actin-based cortical cytoskeleton (Hirano et al., 1987). The association of cadherins with catenins is essential for intercellular Ca.sup.2+ -dependent adhesiveness (Nagafuchi and Takeichi, 1988; Ozawa et al., 1990; Kintner, 1992). .alpha.-catenin is homologous to vinculin (Herrenknecht et al., 1991; Nagafuchi et al., 1991), making it a good candidate for interaction with the actin-based cytoskeleton (see Ozawa et al., 1990; Hirano et al., 1992). .beta.-catenin is homologous to the Drosophilia segment polarity gene armadillo, suggesting a role in developmental signalling in vertebrates (McCrea et al., 1991). .gamma.-catenin is probably identical to plakoglobin (Knudsen and Wheelock, 1992; but see Piepenhagen and Nelson, 1993), which again is homologous to armadillo (see Franke et al., 1989; Peifer and Wieschaus, 1990). Indeed, .beta.-catenin and plakoglobin appear to form a multigene family (Peifer et al., 1992)
A repeating 42 amino acid motif that was originally identified in armadillo (Riggleman et al., 1989) has also been found in several other proteins, including .beta.-catenin and plakoglobin, with a variety of functions (Peifer et al, 1994). These include the APC gene product, a tumor suppressor protein (Kinzler et al., 1991), p120, a pp60.sup.STC substrate (Reynolds et al., 1992), smgGDS, an exchange factor for ras-related G proteins (Kikuchi et al., 1992), a suppressor of RNA polymerase I mutations in yeast (Yano et al., 1992; 1994) and band 6 protein, a major desmosomal constituent (Hatzfeld et al., 1994). The function of the repeats in these arm proteins is unknown. Interestingly, the APC gene product associates with .beta.-catenin (Rubinfeld et al., 1993; Su et al., 1993), supporting an important role for catenins in intracellular processes that regulate cell growth. Furthermore, this illustrates that cadherins are not exclusive cellular partners of catenins, raising the possibility of other interactions among catenins, cadherins and arm proteins, important in a variety of biological processes.
p120 was initially identified as one of several substrates of the tyrosine kinase pp60.sup.src (Reynolds et al., 1989; Kanner et al., 1990). It is membrane-associated and can be myristoylated, but does not appear to be glycosylated (Kanner et al., 1991). Mutational analysis suggested that tyrosine phosphorylation of p120 is necessary for of pp60.sup.STC -mediated cellular transformation (Linder and Burr, 1998/ Reynolds et al., 1989). Tyrosine phosphorylation of p120 was also observed in response to epidermal growth factor, platelet-derived growth factor, colony-stimulating factor 1 and in polyoma virus middle T antigen-transformed cells (Dowing and Reynolds, 1991; Kanner et al., 1991), but the exact role of p120 in cellular physiology and pathology was not clear.